/*
 * @(#)$Id$
 * 
 * Copyright 2006-2008 Makoto YUI
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 * 
 * Contributors: Makoto YUI - initial implementation
 */
package jacky.lanlan.song.io.stream;

import java.io.*;

/**
 * 
 * @author Makoto YUI (yuin405+xbird@gmail.com)
 */
public final class BitInputStream extends DataInputStream {

	public static final int MAX_BITS = 31;

	private int leftBits = 0;

	private int byteBuf = 0;

	public BitInputStream(InputStream in) {
		super(in);
	}

	public final boolean readBit() throws IOException {
		if (--leftBits >= 0) { return ((byteBuf >>> leftBits) & 1) == 1; }
		leftBits = 7;
		byteBuf = in.read();
		if (byteBuf == -1) { throw new EOFException("reached end of stream"); }
		return ((byteBuf >>> 7) & 1) == 1;
	}

	public final int readBits(int n) throws IOException {
		int x = 0;
		while (n > leftBits) {
			n -= leftBits;
			x |= rightBits(leftBits, byteBuf) << n;
			byteBuf = in.read();
			if (byteBuf == -1) { throw new EOFException("reached end of stream"); }
			leftBits = 8;
		}
		leftBits -= n;
		return x | rightBits(n, byteBuf >>> leftBits);
	}

	private static final int rightBits(int n, int x) {
		return x & ((1 << n) - 1);
	}
}
